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Yamaha A-1 Repair and restore: beyond Deoxit

Discussion in 'Yamaha' started by Dadbeh, Jul 2, 2018.

  1. Dadbeh

    Dadbeh Active Member

    Messages:
    423
    i dont see any componenets with discoloration or signs of burn. could the it be the output trans itself? it was real hot.
     

     

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  2. avionic

    avionic " Black Knights " Subscriber

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    At this point I have no idea.Do you know how to check transistors ?
     
  3. Dadbeh

    Dadbeh Active Member

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    423
    i do not
     
  4. avionic

    avionic " Black Knights " Subscriber

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    Time to learn...
     
  5. avionic

    avionic " Black Knights " Subscriber

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  6. avionic

    avionic " Black Knights " Subscriber

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    [​IMG][​IMG]
     
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  7. avionic

    avionic " Black Knights " Subscriber

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    [​IMG]
     
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  8. avionic

    avionic " Black Knights " Subscriber

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    I need to see a close up clear photo of your bias test points..
     
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  9. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    could the it be the output trans itself ? it was real hot.

    No ! if it is really hot , that mean that this TR is good but his bias is not correct at all
    If you don't know how to test a TR it's gone be very difficult to help you from here
    You can't say that a TR is bad if you are looking for any discoloration or signs of burn . A TR can be dead without any external sign .
    I will post a picture from my notes .
    This will help you to do the right things
     
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  10. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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  11. Nashou66

    Nashou66 AK Subscriber Subscriber

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    Check the emitter resistors . They are the large white square ones. 5 watt .47 ohm

    [​IMG]

    Nashou
     
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  12. avionic

    avionic " Black Knights " Subscriber

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    I can't see the emitter resistors being bad without shorted outputs ...
     
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  13. Nashou66

    Nashou66 AK Subscriber Subscriber

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    This was an issue on one of my A-1's I couldn't adjust off set and low volume and distortion. it was the emitter resistors on that channel. I cant remember if it was one or both .

    Nashou
     
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  14. Dadbeh

    Dadbeh Active Member

    Messages:
    423
    three of them measure correctly. one of them is only O.L.

    i had to measure them from under the board from their solder joints.

    thanks for all the info about transistors guys. i read on them and i think im good to take them out and measure them. i was gonna do that tomorrow buyt now im thinking maybe i should replace this resistor first.
     
  15. Dadbeh

    Dadbeh Active Member

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    423
    its one of the ones for the right channel
     
  16. avionic

    avionic " Black Knights " Subscriber

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    OL means "open"
     

     

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  17. Dadbeh

    Dadbeh Active Member

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    well that means it is bad, right?
     
  18. avionic

    avionic " Black Knights " Subscriber

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    Start with the outputs in the right channel.One or both of them may be shorted. Then replace the bad resistor.
     
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  19. avionic

    avionic " Black Knights " Subscriber

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    Right.
     
  20. avionic

    avionic " Black Knights " Subscriber

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